Printing: Fix undefined behavior for near 0 scaling

components/printing/renderer/print_web_view_helper.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/printing/renderer/print_web_view_helper.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <string>
 #include <utility>
@@ skipping 96 matching lines @@
 int GetDPI(const PrintMsg_Print_Params* print_params) {
 #if defined(OS_MACOSX)
   // On the Mac, the printable area is in points, don't do any scaling based
   // on dpi.
   return kPointsPerInch;
 #else
   return static_cast<int>(print_params->dpi);
 #endif  // defined(OS_MACOSX)
 }
 
+constexpr double kEpsilon = 0.01f;

[Lei Zhang, 2016/10/29 01:19:24]

Sorry, I meant line 115 in the header file, that way you can still use the
constant in print_web_view_helper_mac.mm.

CalculatePageLayoutFromPrintParams() will have to change to refer to it as
PrintWebViewHelper::kEpsilon.

[rbpotter, 2016/10/31 16:30:24]

Done.

+
 bool PrintMsg_Print_Params_IsValid(const PrintMsg_Print_Params& params) {
   return !params.content_size.IsEmpty() && !params.page_size.IsEmpty() &&
          !params.printable_area.IsEmpty() && params.document_cookie &&
          params.desired_dpi && params.dpi && params.margin_top >= 0 &&
          params.margin_left >= 0 && params.dpi > kMinDpi &&
          params.document_cookie != 0;
 }
 
 // Helper function to check for fit to page
 bool IsWebPrintScalingOptionFitToPage(const PrintMsg_Print_Params& params) {
@@ skipping 100 matching lines @@
 void CalculatePageLayoutFromPrintParams(
     const PrintMsg_Print_Params& params,
     double scale_factor,
     PageSizeMargins* page_layout_in_points) {
   bool fit_to_page = IsWebPrintScalingOptionFitToPage(params);
   int dpi = GetDPI(&params);
   int content_width = params.content_size.width();
   int content_height = params.content_size.height();
   // Scale the content to its normal size for purpose of computing page layout.
   // Otherwise we will get negative margins.
-  if (scale_factor > 0 && (fit_to_page || params.print_to_pdf)) {
+  if (scale_factor >= kEpsilon && (fit_to_page || params.print_to_pdf)) {
     content_width =
         static_cast<int>(static_cast<double>(content_width) * scale_factor);
     content_height =
         static_cast<int>(static_cast<double>(content_height) * scale_factor);
   }
 
   int margin_bottom =
       params.page_size.height() - content_height - params.margin_top;
   int margin_right =
       params.page_size.width() - content_width - params.margin_left;
@@ skipping 466 matching lines @@
       weak_ptr_factory_(this) {
   PrintMsg_Print_Params print_params = params;
   if (!should_print_selection_only_ ||
       !PrintingNodeOrPdfFrame(frame, node_to_print_)) {
     bool fit_to_page =
         ignore_css_margins && IsWebPrintScalingOptionFitToPage(print_params);
     ComputeWebKitPrintParamsInDesiredDpi(params, &web_print_params_);
     frame->printBegin(web_print_params_, node_to_print_);
     double scale_factor = 1.0f;
 #if defined(ENABLE_PRINT_PREVIEW)
-    if (print_params.scale_factor > 0)
+    if (print_params.scale_factor >= kEpsilon)
       scale_factor = print_params.scale_factor;
 #endif
     print_params = CalculatePrintParamsForCss(
         frame, 0, print_params, ignore_css_margins, fit_to_page, &scale_factor);
     frame->printEnd();
   }
   ComputeWebKitPrintParamsInDesiredDpi(print_params, &web_print_params_);
 }
 
 PrepareFrameAndViewForPrint::~PrepareFrameAndViewForPrint() {
@@ skipping 490 matching lines @@
   const PrintMsg_Print_Params& print_params = print_pages_params_->params;
   const std::vector<int>& pages = print_pages_params_->pages;
 
   if (!print_preview_context_.CreatePreviewDocument(prep_frame_view_.release(),
                                                     pages)) {
     return false;
   }
 
   PageSizeMargins default_page_layout;
   double scale_factor =
-      print_params.scale_factor > 0 ? print_params.scale_factor : 1.0f;
+      print_params.scale_factor >= kEpsilon ? print_params.scale_factor : 1.0f;
 
   ComputePageLayoutInPointsForCss(print_preview_context_.prepared_frame(), 0,
                                   print_params, ignore_css_margins_,
                                   &scale_factor, &default_page_layout);
   bool has_page_size_style =
       PrintingFrameHasPageSizeStyle(print_preview_context_.prepared_frame(),
                                     print_preview_context_.total_page_count());
   int dpi = GetDPI(&print_params);
 
   gfx::Rect printable_area_in_points(
@@ skipping 575 matching lines @@
 void PrintWebViewHelper::PrintPageInternal(
     const PrintMsg_PrintPage_Params& params,
     blink::WebLocalFrame* frame,
     PdfMetafileSkia* metafile,
     gfx::Size* page_size_in_dpi,
     gfx::Rect* content_area_in_dpi) {
   PageSizeMargins page_layout_in_points;
 
   double css_scale_factor = 1.0f;
 #if defined(ENABLE_PRINT_PREVIEW)
-    if (params.params.scale_factor > 0)
+    if (params.params.scale_factor >= kEpsilon)
       css_scale_factor = params.params.scale_factor;
 #endif
   ComputePageLayoutInPointsForCss(frame, params.page_number, params.params,
                                   ignore_css_margins_, &css_scale_factor,
                                   &page_layout_in_points);
   gfx::Size page_size;
   gfx::Rect content_area;
   GetPageSizeAndContentAreaFromPageLayout(page_layout_in_points, &page_size,
                                           &content_area);
   int dpi = static_cast<int>(params.params.dpi);
@@ skipping 491 matching lines @@
       blink::WebConsoleMessage::LevelWarning, message));
   return false;
 }
 
 void PrintWebViewHelper::ScriptingThrottler::Reset() {
   // Reset counter on successful print.
   count_ = 0;
 }
 
 }  // namespace printing